The present invention relates to an arrangement and method for threading elongated material around a rotatable assembly. More particularly, an improved design is provided for an automatic threading process in mounting a gripper arm, a shear, and a material guiding device adjacent to a rotatable drawing block assembly used in pulling wire or tubing through a reducing die, whereby the drawing block does not stop rotating even after the material is placed around the block.
Presently, it is the practice for the cold drawing of metallic strand material, such as wire or tubing, to create the required tension on the material by passing a portion of a single convolution or a greater predetermined length of material around a rotatable block arranged downstream from a die assembly.
At the start of an existing drawing operation, the strand-like material is introduced onto the block into a groove around the block's periphery by providing a gripper which generally is mounted on the block and positionable in line with a reducing die to receive the material as it leaves the die. The gripper grasps the pointed end of the material, and the block with the gripper is rotated approximately 310 degrees at which time rotation is stopped, and the tapered or pointed end is sheared by an externally mounted shearing device which is brought near the block assembly for the shearing operation.
From a design standpoint, there are several disadvantages inherent in this arrangement, i.e. where the gripper arrangement is mounted on the block. The drawing block assembly normally rotates at extremely high speeds thereby increasing (a) the inertia of the system; (b) the braking force necessary for stopping the block; (c) the need for static or dynamic balancing of the components; and (d) the chances of the gripper arrangement being thrown off the rotating block.
From an operational standpoint, a further disadvantage of the aforesaid design where the gripper is mounted on the block assembly and an external shear cuts the tapered end, is that the rotation of the block must be stopped in order to effect the cutting of the tapered end. It is then necessary to remove the gripper from the block or to swing it out of the way of the travelling material, and the shear is moved out of the way of the rotating block. This procedure decreases the production cycle time in the reduction process.
Since the pointed end is sheared in the "threading" or "stringing" up step of the drawing process in the above prior block design, as stated above, the block's rotation is stopped and then started up again for the remaining drawing process. This stopping and starting of the block's rotation in most instances can result in the breakage of the material being drawn.
Another design for a block assembly has evolved where the gripper is detachable from the block, and therefore remains in a stationary position relative to the rotation of the block assembly. The gripper is mounted to an arm, which, in turn is mounted to a bushing on a drive shaft of the block. This arrangement is shown in U.K. Patent Application No. 2,078,583. The arm is freely rotatable and displaceable about the axis of the drawing block and is also selectively drivable by the block through a manually insertable pin for the "threading up" or initial stage of the drawing process. This design eliminates most of the disadvantages associated with the aforesaid arrangement where the gripper is mounted directly onto the block; however, it presents other serious problems in that for the shearing of the pointed end, it is necessary to stop the block so that the shear, which as mentioned is external to the block and gripper, can be brought into position to cut the pointed end. Thus, it is necessary to start the motor to rotate the block, stop it when the material is placed substantially around the block, then start the motor again for the remaining drawing process.
This '583 design may require precise timing and fine tolerances of the mating parts in order for the insertable driving pin to engage the gripper arm and/or block for it to be driven by the main motor of the block's drive system.
A serious disadvantage common to the two above designs in the prior art is in locating the shear relative to the material in a manner that the exact length of pointed end is cut-off with little or no material wastage, i.e. several extraneous devices are positioned around the drum's periphery, making it somewhat difficult to position the shear close enough to sever the desired length of pointed end, which in most instances, is nine (9) inches from the tapered point inwardly along the material. Also, the "threading-up" of both designs require in their most efficient form, considerable manual assistance and utmost loss of production.